1. Field of the Invention (Technical Field)
The invention described and claimed herein relates generally to a method and apparatus for detecting leakage of hydrocarbons from and preventing corrosion of underground storage tanks. More particularly, the present invention relates to field methods and apparatuses for analyzing soil samples taken near an underground storage tank for the presence of hydrocarbons, for measuring the soil-to-tank potential of a tank, for detection of water in a tank, and for protecting a tank from corrosion by supplying current flow through the metal of the tank.
2. Background Art
Thousands of underground tanks storing petroleum products are located throughout the world. With each, a potential for leakage of the stored products exists, and for metal underground storage tanks, a potential for corrosion. Even though an underground storage tank may have a long-term protective coating (e.g., 30-year coating), the tank could get scratched or punctured, particularly during installation, which necessitates periodic testing for leakage.
The area around an underground storage tank must be inspected periodically to determine whether hydrocarbon leakage has occurred. The inspection process heretofore has involved taking soil samples and sending them to a laboratory for inspection. The present invention permits an on-site determination of whether a soil sample is contaminated by hydrocarbons. A laboratory need only be involved to determine the type, amount and possible source of any hydrocarbons detected.
In the prior art, soil samples are collected in the field and then sent to a laboratory for field testing. It is not known in the art to detect the presence of hydrocarbons, using an on-site field kit, with an extraction solvent.
Previously known devices exist in the art which provide for field prospecting for oil deposits by analysis of soil samples. U.S. Pat. No. 2,269,889, to Blau, entitled Process for Locating Valuable Subterranean Deposits, describes a device for locating subterranean deposits of hydrocarbons by field analysis of surface soil samples. The device detects the presence of certain byproducts of hydrocarbon consuming bacteria. A soil sample is combined with water and sodium peroxide, which produces a characteristic color change in the sample if the bacterial byproducts are present. U.S. Pat. No. 2,292,300, to Smith, entitled Photochemical Exploration Method, describes a device for prospecting for hidden petroleum deposits by laboratory analysis of the alkaline salt content of surface soil samples. Soil samples are combined with water and silver nitrate, and the tint of the resulting solution indicates the concentration of alkaline salts within the soil. Anomalies in concentrations may indicate a hydrocarbon deposit below the point or points at which the anomalous sample or samples were taken. These patents do not disclose field testing of soil surrounding underground storage tanks, nor the use of hexane in a soil sample test.
In the laboratory, testing of soil samples generally involves the use of a chlorofluorocarbon extraction solvent which is known to cause environmental problems in its depletion of the ozone layer. It is a purpose of the present invention to use solvents, such as hexane, not known to cause ozone depletion or other environmental problems.
Metal underground storage tanks should also be tested periodically to determine how corroded they are presently, as well as their potential for further corrosion. U.S. Pat. No. 2,839,722, to Marsh, entitled Method and Apparatus for Detecting Stray Current Corrosion, discloses a device for detecting stray voltage in the area of an underground storage tank which may cause the tank to corrode more rapidly. It does not disclose a method or apparatus for measuring what is generally known in the art as "soil-to-tank potential."
Underground storage tanks having a non-minimal potential for corrosion should be protected by inducing current flow through them. This type of protection is generally known in the art as "cathodic protection." U.S. Pat. No. 2,478,478, to Grebe, entitled Potential Gradient Anode for Galvanic Protection, and U.S. Pat. No. 3,168,455, to Shapiro, et al., entitled Corrosion Protection, are examples of methods and devices to reduce the cost of cathodic protection.